In existing gas-turbine combi processes, a supercharger compresses air, which is burned with fuel in a combustion chamber, which is followed by a turbine and a waste-heat boiler, in which water of the secondary-process circulation is vaporized. In the secondary-process circulation there is normally a vapor process, which, in the newest large plants, uses reheating of the water vapor. In the secondary process, after a low-pressure turbine, the water vapor condenses in a condenser into water, which is compressed by a pump to a maximum pressure, and preheated and vaporized in the waste-heat boiler. After the waste-heat boiler, the water vapor goes to the steam turbines of the process circulation.
Using natural gas as the fuel, electricity is nowadays generally produced in a combined gas-turbine-steam power-plant process. Gasified coal is also beginning to be used as a fuel in these. A problem is the large energy requirement for compression and the wasting of a great deal of energy along with the condensation heat of the water vapor. Similarly, in the low-pressure range the efficiency of the water-vapor process is poor and there is no benefit from the second combustion chamber in the gas-turbine combi process. Similarly, the maximum pressure of the gas turbine limits the pressure ratio. At the present moment, the highest efficiency in the world for a combi power plant is 60.7% in the Irsching power plant completed in 2011. The next goal of the manufacturers of the Irsching plant is to achieve 61.5% in 2015, by increasing the initial values.